Various standards have been proposed for the broadband wireless access system, and particularly the IEEE 802.16-2004 and IEEE 802.16e-2005 standards have been approved as the international standards for a portable Internet system. The international standardization group belonging to the IEEE 802.16 is currently standardizing the broadband wireless access system for better performance.
The conventional wireless LAN system based on the IEEE 802.11 standard provides a data communication method available for radio communication within a short range with reference to a fixed access point, which however does not provide mobility of a subscriber station but supports a local area data communication not in a cable manner but in a wireless manner.
The broadband wireless access system defined by the IEEE 802.16-2004 and IEEE 802.16e-2005 standards guarantees mobility and provides a seamless data communication service when a subscriber station moves from a cell controlled by a radio access station to another cell controlled by another radio access station.
The IEEE 802.16-2004 and IEEE 802.16e-2005 standards support the metropolitan area network (MAN) that covers the middle-level areas between the LAN and the WAN.
Therefore, the broadband wireless access system supports the handover of the subscriber station in a like manner of the mobile communication service, and allocates a dynamic IP address as the subscriber station moves.
The international standardization group belonging to the IEEE 802.16 is studying a better wireless portable Internet system with further improved performance compared to the existing broadband wireless access system. Another initial access method between a subscriber station and a radio access station differing from the existing initial access process is required so as to realize a better wireless portable Internet system. Accordingly, a method for realizing an initial access process through various initial access methods between the subscriber station and the radio access station is needed while guaranteeing mutual compatibility with the existing broadband wireless access system.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.